The present invention relates to deodorant fibers, or more specifically, to deodorant fibers suitable as the starting materials for applications including absorptive products such as diapers and napkins, medical and hygienic materials, and materials for home products, general medical products, bedclothes, filters, nursing care goods, and items for pets.
Recent changes in lifestyles, including more closely packed residences and enhanced air-tightness of buildings, have increased needs for odor prevention and/or control. Typical odor sources include basic gases such as ammonia and trimethylamine, sulfur-containing substances such as hydrogen sulfide and methylmercaptan, and lower fatty acids such as acetic acid, lactic acid, valeric acid and caproic acid, which are formed by biodegradation of excretion from the sweat and sebaceous glands. Nitrogen-containing ring compounds such as indole and skatole also are known malodorous substances.
Several methods to remove such odorous substances are known. Typical examples include physical absorption using porous materials such as active carbon or silica gel; chemical methods in which the substances are eliminated by neutralization or oxidation reactions; and sensory methods by which the perception of odor is canceled or masked by a strong perfume. The chemical methods are particularly effective in that they eliminate odorous substances at high concentrations quickly. In fact, a variety of deodorizing agents have been developed.
However, many of the currently used chemical deodorants are effective against ammonia, amines and other nitrogen-containing compounds but not against sulfur-containing compounds, or vice versa. As a matter of fact, few single deodorants are effective against a wide range of odorous substances including lower fatty acids. A variety of improved deodorants have been suggested; examples are a bactericidal and deodorizing agent containing amphoteric surfactants with isoelectric points over 7, amphoteric surfactants with isoelectric points under 7, nonionic surfactants and silicone oil (as in Reference 1); and a liquid deodorant containing as active ingredients betaine amphoteric compounds and ketocarboxylic acids (as in Reference 2). Some complex oxides containing two or more metals also have been proposed that provide an antibacterial or deodorizing activity when a part of the metals are activated (as in Reference 3).
The deodorants mentioned in References 1 and 2 are mostly in the liquid state, and often used as a coating on fiber surface for an effective deodorizing action. Being excellent deodorants in the liquid state, however, those substances usually lose most of their activity when deposited on fiber surfaces, due to attrition by fiber-metal or fiber-fiber friction during fiber opening (e.g. formation of web or sliver in a carding or air laying machine) or by vaporization during the heat treatment for nonwoven fabric manufacture. The final products are effective against ammonia, amines and other nitrogen-containing compounds only.
The deodorants described in Reference 3 are heat-resistant and effective against a relatively wide range of malodorous substances, but, unlike deodorants based on neutralization reactions, they are slow in action and therefore hardly effective against ammonia, amines and other nitrogen-containing compounds.    Reference 1: JP2002-47105    Reference 2: JP2717209    Reference 3: JP11-209258